Optical fiber array alignment unit

ABSTRACT

An optical fiber alignment unit for the easy precise alignment of optical fibers in and array. In a preferred embodiment the positioning array is incorporated twice in an all optical cross connect switch utilizing MEMS mirrors for cross connecting optical fibers in a first set of optical fibers to optical fibers in a second set of optical fibers. The optical fibers are preferably arranged in rectangular arrays. These arrays include array sizes such as 4×8, 16×16 and 8×16. A preferred embodiment built and tested by Applicants is a modular optical switch in which an input 8×16 array of optical fibers from sixteen eight-fiber ribbons are cross-connected into an output 8×16 array of optical fibers also from sixteen eight-fiber ribbons.

The present invention relates to fiber optic communication equipment andin particular to fiber optic switches and fiber optic switch modules.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a companion application to the following relatedapplications filed concurrently with this application: Ser. No.11/728,362, MEMS Mirror Array and Control, Ser. No. 11/728,345, BeamPosition Sensor, Ser. No. 11/728,435, Optical Switch Module, and Ser.No. 11/728,335, Optical Switch with Co-Axial Alignment Beam, all ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION Positioning of Optical Fibers

Optical fibers that carry optical beams typically have dimensionsmeasuring in microns. Often it is necessary to direct light beams intothe extremely small apertures of the fibers or to direct a beam exitingthe fiber. These operations typically require precise positioning of thefiber or fibers.

Fiber Optic Communication

Over the past few decades, the telecommunications industry has exploded,and the incorporation of optical fiber into this industry isrevolutionizing the way information is transmitted. Communicationsystems which use optical fiber as the transmission media offer somesignificant advantages over past copper-based systems. These advantagesinclude higher bandwidths and transmission rates, lower transmissionlosses, and greater signal isolation. There exist in the United Statesmany million miles of optical fibers. Information must be routed throughthis maze of fibers at the speed of light from millions of transmittersto millions of receivers.

Fiber Optic Multiplexing and De-Multiplexing

In a typical fiber optic communication system several fibers may bebundled together with many separate signals combined within the lightbeam carried in each of the fibers in the bundle. This combination ofseparate signals into a single beam carried by a single fiber is calledmultiplexing the signals. Both time division and frequency divisionmultiplexing may be utilized. In typical fiber optic systems each signalcarries with it a code so that traffic controls in the system can directthe signal to its proper destination. Light beams comprised of manysignals typically travel serially through several or many fibers beforereaching its sub-destination or final destination. Individual signalsare collected into a single fiber in a process called multiplexing andseparated out from other signals in a beam in processes calledde-multiplexing. This operation may occur once or several times duringthe transit of information in the form of these light signals fromsender to receiver.

FIG. 13A depicts de-multiplexing and FIG. 13B depicts multiplexing. FIG.13C shows a prior art static cross connection with two de-multiplexersand two multiplexers showing how signals carried at four separatewavelength ranges on two separate fibers can be switched to two otherfibers. Optical filters that transmit a single wavelength range andreflect all other wavelength ranges are often used to separatewavelength ranges in multiplexers and de-multiplexers. A well knownfilter is the thin film filter as shown in FIG. 13D. These filters aretypically built up on a glass substrate with thin films of one or moresets of ¼ wave dielectric reflectors on both sides of a ½ wave cavity.FIG. 13E shows the result of one, two and three sets of ¼ wavereflectors and ½ wave cavities. FIG. 13F shows how these narrow bandfilters can be used to produce a de-multiplexer. A multiplexer resultsfrom switching the directions indicated by the arrows.

Adjusting Fiber Routes

Traffic controls can route a particular signal from sender through manyfibers to the receiver without changing the way the various opticalfibers of the system are connected. However, as particular fiber routesbecome crowded, the connections between fibers must be modified toreduce the crowdedness or to route the signals more efficiently. This isthe job of the fiber optic switch. This operation can be done bychanging the actual connections between fibers in a fiber switch unit.Historically, fast switching of optical-beam routes through opticalfibers has been accomplished using hybrid optical-electrical-opticalswitches for detection and conversion of optical signals entering theswitch from a first fiber to an electrical signal that is used toproduce a new optical signal for transmission over a second opticalfiber.

MEMS Mirrors

MEMS mirrors are lithographically produced mirrors that are operatedwith voltage signals applied through integrated circuits produced withsimilar lithographic techniques. These mirrors typically are very tinyhaving dimensions measured in millimeters or fractions of millimeters.They are designed with extremely tight tolerances necessary for properangular alignment of the various reflective elements, and usuallyrequire very sophisticated feedback control systems.

Automatic All Optical Cross Connect Switches

Recently, a number of optical cross connect switches have becomeavailable for switching optical signals directly from one fiber toanother, thereby eliminating the need to convert the optical signal toan interim electrical signal. These optical switches incorporate variousoptical switch elements, such as mirrors, prisms, fiber collimators, andcomplicated drive mechanisms, to route optical signals through theswitch. For some optical switches, MEMS mirrors have been utilized. Alloptical switches are described in the following patents recently issuedwhich contain features similar to some of the features of the presentinvention: U.S. Pat. No. 7,190,509, Optically Addressed MEMS and U.S.Pat. No. 7,177,497, Porous Silicon Filter for Wavelength Multiplexingand De-Multiplexing, both of which are incorporated herein by reference.

Applications of All Optical Automatic Cross Connect Switches

Known uses of all optical cross connect switches include (1) use as theprincipal component in a automated fiber patch panel, (2) use acomponent of a reconfigurable optical add drop multiplexer (ROADM)system and (3) use for automatic testing and measurement of opticalcomponents and systems.

Automated Fiber Patch Panel

Automated fiber patch panels are the components of a fiber opticcommunication network where communication routes are established andmodified. These panels can be computer controlled to maintain networkefficiency, to avoid overload and to respond quickly to faultsituations.

Reconfigurable Optical Add Drop Multiplexers

When individual fibers are carrying many separate signals, the networkmust provide for adding new signals to the fiber and extracting(dropping) other signals. FIG. 13G shows an add-drop unit comprised ofmultiplexers and de-multiplexers but no switch. This unit would beconsidered a static unit and requires an operator to reconfigure it.FIG. 13H is a similar unit but with an optical switch that can beremotely operated or programmed to operate automatically. This unitincludes tunable transponders permitting control of the wavelengthsadded. FIG. 13I shows a ROADM comprising four separate optical switchesfor switching signals among fibers as well as controlling the adding anddropping of signals for local service.

Test and Measurement

Automated all optical cross connect switches can greatly simplifytesting of optical components especially components of typicalcommunication networks simultaneously carrying millions of messages.

The Need

A need exist for a method and unit for easy and precise alignment ofoptical fibers in an array.

SUMMARY OF THE INVENTION Optical Fiber Array Alignment Unit

The present invention provides a technique and optical fiber alignmentunit for the easy precise alignment of optical fibers in and array. In apreferred embodiment the positioning array is incorporated twice in anall optical cross connect switch utilizing MEMS mirrors for crossconnecting optical fibers in a first set of optical fibers to opticalfibers in a second set of optical fibers. The optical fibers arepreferably arranged in rectangular arrays. These arrays include arraysizes such as 4×8, 16×16 and 8×16. A preferred embodiment built andtested by Applicants is a modular optical switch in which an input 8×16array of optical fibers from sixteen eight-fiber ribbons arecross-connected into an output 8×16 array of optical fibers also fromsixteen eight-fiber ribbons. In the preferred embodiment the opticalfibers in the first set of optical fibers are precisely positioned in afirst fiber-microlens positioning array to define a first set ofparallel collimated cross-connect communication beam paths, with eachcollimated cross-connect communication beam path connecting an opticalfiber in the first set of optical fibers with a MEMS mirror in a firstMEMS mirror array. The optical fibers in the second set of opticalfibers are precisely positioned in a second fiber-microlens positioningarray to define a second set of parallel collimated cross-connectcommunication beam paths, with each collimated cross-connectcommunication beam path connecting an optical fiber in the second set ofoptical fibers with a MEMS mirror in a second MEMS mirror array. Theseparallel collimated beam paths establish a correspondence between thefirst fiber-microlens positioning array and the first microlens arrayand a correspondence between the second fiber-microlens positioningarray and the second microlens array so that each optical fiber in thefirst positioning array has its own corresponding microlens in the firstmicrolens array and each optical fiber in the second positioning arrayhas its own corresponding microlens in the second microlens array.

MEMS Mirror Arrays

The cross connect switch of the present invention includes two MEMSmirror arrays. In preferred embodiments each of the MEMS mirrors aredriven in two axes by vertical comb drive actuators.

Co-Axial Alignment Beams

A first set of alignment beams are added to and aligned co-axially witheach of the first set of parallel collimated cross-connect communicationbeams. A second set of alignment beams are added to and alignedco-axially with each of the second set of parallel collimatedcross-connect communication beams.

Dichroic Mirror

In preferred embodiments of the present invention a dichroic mirror ispositioned to reflect communication beams from MEMS mirrors in the firstMEMS mirror array and to reflect cross connect communication beams fromMEMS mirrors in the second MEMS mirror array and to transmit the firstset of alignment beams and the second set of alignment beams.

MEMS Control System

A MEMS control system is provided to position the MEMS mirrors in thefirst and second MEMS mirror arrays to optically connect any of theoptical fibers in the first set of optical fibers to any optical fiberin the second set of optical fibers. In preferred embodiments the MEMScontrol system is adapted to position each MEMS mirror in the first MEMSmirror arrays so as to reflect the cross connect communication beamsfrom its corresponding fiber in the first set of optical fibers off thedichroic mirror and onto to a MEMS mirror in the second set of MEMSmirrors corresponding to a any selected optical fiber in the second setof optical fibers and to position the corresponding MEMS mirror in thesecond set of MEMS mirrors to direct the communication beam to itscorresponding optical fiber in the second set of optical fibers. Inpreferred embodiments the mirrors are controlled by adjusting voltagepotentials applied to the comb drive actuators of the individual mirrorsin order to establish desired optical communication paths betweenoptical fibers in the first set of optical fiber and the second set ofoptical fibers.

Beam Direction Sensors

In preferred embodiments the MEMS control system includes a first beamdirection sensor unit positioned to detect each alignment beam in thefirst set of alignment beams transmitted through the dichroic mirror anda second beam direction sensor unit positioned to detect each alignmentbeam in the second set of alignment beams transmitted through thedichroic mirror. In a particular preferred embodiment each of the beamdirection sensor units each includes an alignment beam detection screenand a video camera for viewing the position of the intersections of thealignment beams with the unit's viewing screen. In these embodiments theMEMS control system includes a processor programmed to provide a closedloop adjustments of pairs of MEMS mirrors (one from each of the two MEMSmirror array) in order to determine appropriate voltage potentials to beapplied to the comb drive actuators in order to provide each desiredoptical path between the two sets of optical fibers. Applicants' testshave shown that once the calibration has been performed there is verylittle drift in the beam paths under normal conditions. However,significant changes in environmental conditions could require arecalibration. In some embodiments the switch could be adapted toautomatically re-calibrate itself periodically or at the direction ofoperating personnel.

V-Groove Fiber-Microlens Positioning Arrays

In preferred embodiments the first and second fiber-microlenspositioning arrays include a positioning plate withlithographically-defined sub-micron V-groove alignment features foralignment a set of ribbon optical fibers. The fibers are firstpositioned in the V-grooves, then glued in place after which the ends ofthe fibers are polished smooth with the exit surface of the positioningplate and matched with a micro lens array to provide the fiber-microlens positioning array with sub-micron positioning accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prospective view of a preferred embodiment of the presentinvention with alignment cameras in place.

FIGS. 1A and 1B show features of an alignment beam insertion component.

FIGS. 2A and 2B respectively show a prospective and a top view ofportions of the preferred embodiment of the present invention.

FIGS. 3A, 3B and 3C show additional alignment beam features and testresults.

FIG. 4 shows the size of the preferred embodiment in its modular formrelative to an adult human hand.

FIGS. 4A, 4B and 4C respectively show the preferred module utilized in aRODAM application, a patch panel application and a test and measurementunit.

FIGS. 5A, 5B and 5C show optical paths in a preferred optical switch.

FIGS. 6A, 6B and 6C show features of a preferred V-groovefiber-microlens positioning array.

FIG. 7 shows a MEMS driver control circuit.

FIG. 8A shows a MEMS mirror array designed by applicants.

FIGS. 8B, 8C and 8D show magnified portions of the MEMS mirror array.

FIGS. 9A through 9K demonstrate important lithography steps used to makeone of the vertical comb drives for the MEMS mirror in the MEMS mirrorarray.

FIG. 10 shows a control system.

FIG. 11 shows a nationwide fiber optic network.

FIGS. 12A through 12J show concepts for using porous silicon filters formultiplexing and de-multiplexing.

FIG. 13A through 13I show prior art multiplexing techniques.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Preferred Embodiment

FIG. 1 shows at 2 a prospective view of features of a first preferredembodiment of the present invention. This first preferred embodiment isan optical switch module 2. Its size and general shape is described bythe drawing in FIG. 4 as compared to a adult human hand. This opticalswitch module 2 is designed for switching optical communication beamscarried by the fibers of a first 128 (8×16) optical fiber bundle such asbundle 4 as shown in FIG. 1 into the fibers of a second 128 opticalfiber bundle such as bundle 6. The beams in any fiber of bundle 4 can beswitched into any fiber of bundle 6. The switch is symmetrical and canbe operated in either direction so that any fiber of bundle 6 can beswitched into any fiber of bundle 4.

We sometimes refer to the fibers in bundle 4 as being the input fibersand the fibers in bundle 6 being the output fibers, recognizing that theswitch works just as well with the fibers in bundle 6 being the inputfibers and the fibers in bundle 4 being the output fibers. Also, in somecases a single fiber link could have communication beams flowing in bothdirections at the same time. In addition in some configurations linksbetween fibers in bundle 4 and bundle 6 could be 4 to 6 for some fibersand 6 to 4 in other fibers. In this specification and in the claims,Application refer to the light beams carried by the optical fibers as“communication beams” primarily to distinguish them from the “alignmentbeams” but there may be applications of the present invention where thebeams carried by the optical fibers may not be generally considered ascommunication beams in the normal sense because they are notspecifically carrying information from one place to the other.Nevertheless, for purpose of this specification and the claims, alllight beams carried by the optical fibers in bundles 4 and 6 are to beconsidered as communication beams.

This module is designed for easy integration into a line card forinsertion into a standard communication panel in a reconfigurableadd—drop application as shown in FIG. 4A. The module can be utilized ina patch panel as shown in FIG. 4B and can be utilized in a largenation-wide communication system such as the one discussed in thesection of this description entitled “Application in a Nation ScaleFiber Optic Network” in which each fiber is carrying information at alarge number of separate frequencies. The switch is also useful as atool for component testing and system monitoring by installation in atest and measurement panel as shown in FIG. 4C.

Important components of the preferred embodiment shown in FIGS. 1 and 2are alignment beam units 10 and 12, dichroic beam splitter 14 andalignment screen and camera units 16 and 18 and MEMS mirror arrays 20and 22.

Fiber-Microlens Positioning Array

The optical fibers in the first set of optical fibers are preciselypositioned in a first fiber-microlens positioning array unit 8 as shownin FIGS. 2A and 2B to define a first set of parallel collimatedcross-connect communication beam paths, with each collimatedcross-connect communication beam path connecting an optical fiber in thefirst set of optical fibers with a MEMS mirror in a first MEMS mirrorarray. The optical fibers in the second set of optical fibers areprecisely positioned in a second fiber-microlens positioning array 10 todefine a second set of parallel collimated cross-connect communicationbeam paths, with each collimated cross-connect communication beam pathconnecting an optical fiber in the second set of optical fibers with aMEMS mirror in a second MEMS mirror array.

FIGS. 6A, 6B and 6C show features of a preferred fiber-microlenspositioning array units. In the preferred switch each of the twofiber-microlens positioning arrays and each of the two microlens arraysdefine matching 8×16 matrices that Applicants have labeled 1-1 beginningat the top left as shown in FIG. 3C to 16-8 at the bottom right. Some ofthe corresponding matrices numbers are shown on the micro-lens drawingin FIG. 8B. These parallel collimated beam paths establish acorrespondence between the first fiber-microlens positioning array andthe first microlens array which are similarity labeled and acorrespondence between the second fiber-microlens positioning array andthe second microlens array so that each optical fiber in the firstpositioning array has its own corresponding microlens in the firstmicrolens array and each optical fiber in the second positioning arrayhas its own corresponding microlens in the second microlens array. Inpreferred embodiments the first and second fiber-microlens positioningarray units are identical.

V-Groove Position Plate

Details of these preferred fiber-microlens positioning arrays aredescribed in FIGS. 6A, 6B and 6C. These units are designed to easily andprecisely position optical fibers in sixteen standard eight fiberribbons with fibers having 125 micron cores. In FIG. 6B the ribbons areshown at 4A, individual fibers are shown at 4B and the bundle of fibersare shown at 4. Positioning plate 7A is comprised of a plate comprisedof silicon that has been fabricated using lithographic techniques. Plate7A is mounted on mounting plate 7B which contains mounting slots formounting the fiber-microlens array unit in the optical switch module.Elongated horizontal slots 8 are provided for the eight fibers in eachor the 16 ribbons. Precision V-groves slots 8A are cut in the bottom ofelongated slots 8 These slots have 250 micron wide vertical sides 8Bwith a 45-degree V section 8C at the bottom of the groove, all as shownin FIG. 6A. The slots are on 2 millimeter centers in the horizontaldirection and the slots are on 1 millimeter centers in the verticaldirection. The V-groove slots in each row are off-set from the slots intheir closest neighbor row or rows as shown in FIG. 6B, so the arraycross-section dimension is 15 millimeters×15 millimeters. In thesepreferred embodiments the individual fibers are inserted into the slotsand are precisely located in the V-grooves and glued in place. After thefibers are solidly located the ends of the fibers are cut and then theprotruding and excess glue are polished away to obtain a preciselyperpendicular exit surface for each fiber. (The reader should note thatApplicants use the phrase V-groove in this specification and the claimsto mean a groove with the general shape of a V not necessarily with theprecise shape of a V (i.e. a groove with space at the top substantiallylarger than the space at the bottom). The grooves is however positionedwith precision in the array.

Micro-Lens Array

In these preferred embodiments an 8×16 microlens array 9, alsofabricated with precision using lithographic techniques is provided withthe microlens array precisely positioned to correspond to the positionof the fibers in the V-grove position plate. Each lens has a diameter ofabout 1.1 millimeter and a focal length of 3.7 millimeter. Precisionspacers not shown are used to position the microlens array so that thelenses are positioned about 3.7 mm from the ends of the fibers in theV-groove position plate. When positioning microlens array 9 the finalprecise location is chosen so that the waist of communication beamspassing through the switch from one fiber bundle to the other is locatedas close as reasonably feasible to dichroic mirror 24 as shown in FIG. 1and FIGS. 5A, 5B and 5C.

Co-Axial Alignment Beams

Preferred embodiments of the present invention include provisions forproviding alignment beams aligned co-axially with each of the beamsexiting each fiber in both of the fiber bundles 4 and 16. A particulartechnique for providing these alignment beams is shown in FIGS. 1, 1Aand 1B alignment techniques are described by reference to FIGS. 5A, 5Band 5C. As shown in FIG. 1 this preferred embodiment includes alignmentunit 10 for aligning communication beams from fiber bundle 4 andalignment unit 12 for aligning communication beams from fiber bundle 6.Alignment unit 12 is also shown in FIG. 1A and a cut away drawing of itis shown in FIG. 1B. Unit 12 includes an injection unit 12A with a“point” visible light source shown at 12F such as a vertical cavitysurface emitting laser (VCSEL) operating in the near infrared at 850 nmand having a divergence of about 30 degrees. The beam from this sourceis collimated with collimator optics 12A to produce a collimated beamwith a cross sectional dimension of about 16 millimeter×16 millimeters.This collimated beam is separated into 128 separate beams with mask 12Chaving 128 0.6 mm diameter apertures that are positioned to align the128 separate parallel beams with the communication beams from fiberbundle 6. The actual alignment occurs at dichroic beam splitter 12D thatpasses the communication beam and reflects the alignment beams.

MEMS Mirror Beam Control

In preferred embodiments communication beams are directed within theswitch module with two MEMS mirror arrays 20 and 22. The two arrays areidentical. MEMS mirror array 20 is shown in FIG. 8A. The position of themirrors correspond precisely to the positions of the fibers and themicrolenses in fiber-microlens array unit 8 and 10. An expanded drawingof the top left corner of FIG. 8A is shown in FIG. 8B and a furtherexpanded drawing of one of the mirrors (mirror 3-1) is shown in FIG. 8C.FIG. 8D shows an even further expansion of one of the vertical combdrives, drive 60, of one of the FIG. 8C mirrors. Techniques forproducing MEMS mirrors are well known and well reported in the priorart. The MEMS mirrors of the present invention include special featuresadapted to produce the excellent performance of preferred embodiments ofthe present invention. As shown in FIG. 8C a gold reflecting surface 80of each MEMS mirror can be pivoted about two axes, a first axis 82 aboutwhich pivots inner frame 84 and a second axis 86 about which reflectingsurface 80 pivots. Comb fingers attached to the axels are positionedbelow “stationary” fingers (shown white in FIGS. 8A, 8B and 8C) attachedto the frames. Electrical potentials of 0 to 200 volts causes the lowerfingers to be pulled up between the “stationary” fingers causing themirror surface to pivot about it respective axes.

Fabrication Techniques for Comb Drives

A special preferred technique for producing the comb drives for the MEMSmirrors shown in the figures is described with respect to FIGS. 9Athrough 9K. As indicated in FIG. 9A the process starts with a wafer oftwo 25 micron thick layers 30 and 32 of single crystal silicon on a 380micron thick single crystal silicon handle layer 34. The three layers ofsilicon are separated by a 1.5 micron buried oxide insulator 36 and a0.5 micron buried oxide insulator layers 38. The silicon layers are alldoped to reduce their electrical resistivity to the range of about 10 to20 milli-ohm centimeters. A SiO2 layer 40 is added as shown in FIG. 9Bwhich is patterned using photo resist and a contact mask to produce thepattern 42 shown in FIG. 9C. Next as shown in FIG. 9D a resist mask 44is applied covering part of oxide pattern 42 as shown in 9D. Thismodification of mask pattern 42 is a very important step since it andsome following steps will assure that the extremely thin comb elementsin this comb drive will be properly aligned. For as shown in FIG. 9E,the mask laid on in FIG. 9D is used to etch away part of the oxidepattern laid down in the FIG. 9C step. Next as shown in FIG. 9F a deepreactive ion etch is used to etch silicon layer 30 using the same maskpattern 44. After this etching step has completely removed the siliconbetween the wafer surface and oxide layer 36 the photo resist applied inthe FIG. 9D step is removed as shown in FIG. 9G. A blanket oxide etch isapplied to remove all exposed buried oxide while leaving enough of themodified mask 42 to protect the silicon beneath it form the subsequentsilicon etching step shown in FIG. 9J. Next backside etches are appliedto remove most of handle 34 and oxide layer 38 under silicon layer 32 asshown in FIG. 9I. Then as shown in FIG. 9J the wafer is temporallymounted on a handle wafer and the unprotected portions of silicon layers30 and 32 are etched away. And an oxide etch is applied to remove theoxide layers form the tops of the comb fingers to leave the comb fingersas shown in FIG. 9K. The tall fingers 50 are a part of the frame of theMEMS mirror and will be a fixed part of the MEMS frame or the centralframe element of the MEMS mirror. The short fingers will be move withthe mirror element as potential is applied as discussed later. The tallfingers are shown in white in FIG. 8D at 50 and the short moving fingersare shown in black at 52 in FIG. 8D outlined in a thin white line. Theseare the fingers that rotate with the gold mirror surface 80 of the MEMSmirror as shown in FIG. 8C.

The reader should note that the tall fingers 50 are divided into twoconductive silicon parts 47 and 43 by insulating layer 45. Duringcontrol of the MEMS mirrors electrical potentials of between 0 and 200volts are applied between silicon parts 47 of the tall “stationary”fingers and the short moving fingers 52. This produces an attractiveelectrical force pulling moving fingers 52 up in between silicon parts47 of the tall “stationary” fingers in order to tilt the reflectingmirror surface.

Control of the MEMS Mirrors

A preferred circuit for controlling the MEMS mirrors is shown in FIG. 7.Two circuits are needed for each comb drive unit. There are two combdrive units for each of the two axes for each of the 128 mirrors. Sothis embodiment requires 1024 circuits to control the 128 mirrors. Thegood news is that the components of the circuits shown in FIG. 7 arevery inexpensive, only a few cents for all of the components. Thecircuit is provided with a 200 volt bias as shown in the figure. This200 volt bias charges capacitor C2 only when transistor X19 is in an“off” state. When transistor X19 is “on” there is a discharge pathbetween capacitor C2 and the ground node. Transistor X19 is turned onand off with two kilohertz pulse width modulator indicated on thedrawing as “2 Khz PWM” which in turn is controlled (in Applicants'prototype unit) by a field programmable gate array or a programmablelogic device (both not shown). The electric potential on capacitor C2determines the position of one of the comb drives of one of the MEMSmirrors. The potential can be any potential between 0 volts and 200volts. The potential on capacitor 2C depends on the modulation of the 2Khz pulse width modulator shown in FIG. 7. If the width of each of the2,000 pulses per second is maximum, transistor X19 will be “on”continuously and the voltage on C2 will be approximately zero. If thewidth of each of the 2,000 pulses per second is minimum, transistor X19will be “off” continuously and the voltage on C2 will be approximately200 volts. The pulse width can be varied between minimum and maximum tovary the voltage potential on capacitor C2 from 200 volts to zero volts.The tilt of MEMS mirrors such as MEMS mirror 3-1 depends on the voltageapplied to the four vertical comb drive units controlling the positionof each mirror.

Each of the MEMS mirrors has sufficient range to direct beams as neededto connect any of the fibers in bundle 4 to any of the fibers in bundle6.

Beam Direction Sensors

In preferred embodiments the MEMS control system includes a first beamdirection sensor unit 16 as shown in FIG. 1 positioned to detect eachalignment beam in the first set of alignment beams transmitted frominjection unit 10 co-aligned with communication beams from fiber bundle4, reflected from MEMS mirror array unit 20 and transmitted through thedichroic mirror 14. The embodiment also includes a second beam directionsensor unit 18 positioned to detect each alignment beam in the secondset of alignment beams transmitted from injection unit 12 co-alignedwith communication beams from fiber bundle 6 and transmitted through thedichroic mirror 14. In a particular preferred embodiment each of thebeam direction sensor units each includes an alignment beam detectionscreen 60 and 62 and a video camera 64 and 66 for viewing the positionof the intersections of the alignment beams with the unit's viewingscreen. The screen can be any of a wide variety of screens that producean image when illuminated with an alignment beam. FIG. 3B shows testresults produced with a variety of screen candidates. Results areplotted as a function of mirror angle. FIG. 3A shows a typicalillumination pattern viewed from the side of the screen opposite thebeam intersection side. These include frosted glass and variousdiffusers. A preferred screen is a holographic diffusers supplied byLuminit with offices in Torrence, Calif. FIG. 3 provides an illustrationof the beam direction sensor system. The reader should note that thescreen in this preferred embodiment will be adapted to detect 128 beamswith an 8×16 pattern corresponding to the mirror arrays 20 and 22 andthe fiber-microlens arrays 8 and 10.

In these embodiments the MEMS control system includes a processorprogrammed to provide a closed loop adjustments of pairs of MEMS mirrors(one from each of the two MEMS mirror array) in order to determineappropriate voltage potentials to be applied to the comb drive actuatorsin order to provide each desired optical path between the two sets ofoptical fibers. Applicants' tests have shown that once the calibrationhas been performed there is very little drift in the beam paths undernormal conditions. However, significant changes in environmentalconditions could require a recalibration. In some embodiments the switchcould be adapted to automatically re-calibrate itself periodically or atthe direction of operating personnel.

Directing the Beams

FIGS. 5A, 5B and 5C show some simple illustrations of the operation ofthe preferred embodiment described in detail above. FIG. 5A illustratesthe connection of a fiber column 1 of bundle 1 with a fiber in column 8of bundle 6. The reader should note that camera 64 and 66 detect theco-aligned alignment beams passing through dichroic mirror 24 to providefeedback to the MEMS mirror control to adjust positions of the MEMSmirrors to assure that the beam path is the correct one. FIG. 5Bdemonstrates a connection between the same input fiber and a fiber inone of the columns near the center of the fiber-microlens array and FIG.5C demonstrates a connection between the same input fiber and a fiber incolumn 1 of the fiber-microlens array. The reader should not theposition of the alignment beam in FIGS. 5B and 5C.

Application in a Nation Scale Fiber Optic Network

U.S. patent application Ser. No. 10/677,590 that has been incorporatedherein by reference describes a nation-scale high speed communicationnetwork that utilizes all optical switches. The switches describedherein would work very well in a network like the ones described in thatapplication. In the preferred embodiment described in the '590application, the center wavelength of the beams in each fibers is about1.57 micron (corresponding to 193.1 THz) with a usable bandwidth of15,000 GHz (between 186,000 GHz to 201,000 GHz). As many as 300 separatecommunication channels (at 50 GHz each) may be carried in the beam ineach fiber. Each of the 300 separate channels (at 50 GHz each) can bedivided up into still smaller frequency ranges such as six sub-frequencyranges with 4 GHz spacings. This would permit 1200 signals to betransmitted simultaneously in each fiber, so with 256 fibers per bundle,we could theoretically transmit more than 300,000 separate signalssimultaneously per fiber bundle. These signals must be inputtedseparately at transmit locations to produce the combined beams andseparated out from all other signals to be received by each signalrecipient. This is referred to as frequency division multiplexing Timedivision multiplexing permits additional multiplication of the number ofseparate communications that can be handled during any particular timeperiod.

FIG. 11 is a modified version of FIG. 1 from the '590 patentapplication. Here we consider a nation-scale network with end usersassigned to one of 250 area codes with roughly equal numbers of endusers in each. For instance, area code #1 has been assigned to SanDiego, #40 to Seattle, #200 to Washington D.C., and #240 to some subsetof international users. The proposed network can have about 400,000 UserNodes per Area Code. As seen in FIG. 1, optical cross-connect switches2K associated with each area code are located at mesh nodes 4K tiedtogether in a mesh network which allows switching of optical signalsfrom any particular area code to any other area code. The particularmesh network would make maximum use of intercity fiber trunk lines whichhave already been installed.

In this preferred embodiment all long haul communication is throughoptical fibers operating in the wavelength range centered at about 1.57micron (corresponding to about 193.1 THz). The network is designed tooperate at frequencies between 186 THz to 201 THz for a total bandwidthof 15,000 GHz. At 50 GHz spacings, this provides 300 “color” channelsper optical fiber. Four separate fibers provide a total of 1200communication channels.

There are in this embodiment 1200 separate wideband communicationschannels (each with 15 GHz of useable optical bandwidth) leaving andentering each area code. We call these wideband channels FiberColors,and they are distributed as 300 different DWDM wavelengths (standard 50GHz spacing) on 4 separate fibers. The preferred optical networkoperates in the C and L bands at a center frequency at 1570 nm (193.1THz). Thus there are eight lit fibers between an Area Code and itscorresponding switch, four for outgoing traffic and four for incomingtraffic as shown at 6K on FIG. 11.

If we divide 1200 FiberColors by the number of area codes (300) we havean average of 4.8 FiberColors per area code. However, the 1200 outgoingFiberColors from any particular area code (say San Diego) are allocatedbased on usage demand to the 250 area codes with a total bandwidth ofabout 15 THz per fiber. For instance, the FiberColors for traffic fromSan Diego might be allocated at a particular time as follows: ten fortraffic to Washington, six for traffic to Seattle, one for traffic toAtlanta, etc., until all 1200 FiberColors are accounted for. It isexpected that the actual allocation will be automatically adjustedperiodically as demand shifts with time of day and day of the week.Therefore, at any particular time, the switches must be configured sothat each FiberColor from each origination area code is guided throughthe network to its destination area code without interference. (That is,the same fiber cannot be used simultaneously for two FiberColorsoperating at the same wavelength). It was not immediately obvious thatthis could be done, but applicants have developed an algorithm foraccomplishing this task which appears to be robust and to converge in apractically short time. We call this algorithm a Magic Square Algorithm,because the underlying matrices of FiberColors which need to beallocated have rows and columns which add up to the same number. Thisproblem of allocating FiberColors along with its solution is discussedin detail in the section of this specification entitled “Magic SquareSoftware.” The solution of this problem is a key technical innovation,as it enables the deployment of a nation-scale all-optical network witha relatively small number of channels without the disadvantages ofhaving to convert any optical signal to an electrical signal or toanother DWDM wavelength between the data source and the data destinationarea codes.

Operation of the switches 2K at the Mesh Nodes 4K is discussed in moredetail in the '509 patent application. In preferred embodiments, allDWDM wavelengths are de-multiplexed before optical switching, and thenre-multiplexed after switching. No wavelength separation is required ata resolution finer than the standard 50 GHz DWDM spacing, so thatstandard components can be used. (Finer channel resolution only occurswithin the source and destination area codes). Customized switches whichcombine wavelength separation with the optical switching may also bepossible. Optical Amplifiers (such as erbium doped fiber amplifiers) areused throughout the network as necessary to maintain appropriate opticalsignal strength.

Other Control Techniques

Referring now to FIG. 10, a block diagram of the control system of theOptical Cross Connect Switch of the present invention is shown andgenerally designated 400. Control system 400 includes a computer 402containing a real time computer 404, a telecommunications interface 406,and a digital storage device 408. Computer 402 is a system capable ofmaking the computations required to implement a closed-loop feedbackcontrol system. It may be comprised of analog or digital electronics, ormay be implemented with optical computations units. In a preferredembodiment, the computer consists of digital electronics with at leastone component capable of computation, and with at least three digitalinterfaces. The first interface would be capable of receiving thedigitized optical feedback signals, the second interface would becapable of transmitting command signals to the analog electronic driverrequired for actuation of beam directors 16 and 18. And the thirdinterface would be capable of receiving the network configurationcommand from an external source and transmitting the state of theoptical switch. Other interfaces may be required for certainimplementations.

In a preferred embodiment, the digital computation electronics couldconsist of one or more general purpose processors, such as a commercialavailable digital signal processor or other central processing unit, ormight be one or more application specific integrated circuits designspecifically for this task. The digital interfaces could consist of anyone of a large variety of parallel or serial links and may conform tosome industry standards, or may be custom for a particularimplementation.

Telecommunication interface 406 provides an electronic interface betweencomputer 402 and a telecommunication exchange via interconnect 410. In atypical environment incorporating the switch of the present invention,interconnect 410 will receive switching information, including the inputfibers and the output fibers, which are to be optically coupled. Astandard format for receiving this information may be established by aparticular telecommunications network, but it is to be appreciated thatregardless of the particular protocol, this information will containparticular switch configurations which may be implemented by the presentinvention.

Digital storage device 408 may include both temporary and permanentdigital memory media. For example, digital storage device 408 mayinclude random access memory for manipulation of data, and programmableread only memory for storage of programmed computer sequence steps, andmay include tables of offset values.

Computer 402 is electrically connected to digital interface 414 viaelectrical connection 412. Digital interface 414 contains high voltageamplifiers, and digital to analog converters that convert digitalinformation from computer 402 to the analog signals necessary to controlthe mirror elements. Digital interface 414 also transmits and receivesany necessary digital data between computer 402 and beam directors 420.(The reader should not that for simplicity FIG. 8 shows only one mirrorand one sensor and should recognize that each cross connection beam iscontrolled by the positioning of two mirrors and beam directions aremonitored by two sensors. However, a preferred technique for maintainingbeam position is to adjust only one mirror at a time. It will often benecessary to tweak one mirror in a beam path then tweak the other oneseveral times before perfect control is established. This can all beprogrammed to occur automatically or as directed by an outside controldevice or operator.

The pivot controls for a single MEMS mirror receive the electronicsignals from interface 414 and drive the MEMS mirror its two particularrotational positions in order to direct cross-connect beam in itsdesired directions. In order to ensure that the MEMS mirrors areproperly positioned, the optical sensors measure the position of thealignment beam and provide optical feedback as described above. Analoginterface 426 contains analog signal conditioning components, includinganalog amplifiers and analog to digital converters, which receive theanalog signals from optical sensor 422 and generate digital signals fortransmission along electrical connection 428 to computer 402. Computer402 receives the electronic information from sensor 422 regarding theposition of the alignment beam, and compares this position to theposition contained in the memory 408 to determine whether the beamdirector elements 420 in beam directors 16 and 18 are properlypositioned. If there is a difference between the position of thealignment beam measured by sensor 422 and the position data contained inmemory 408, computer 402 adjusts the electronic signals sent to digitalinterface 414 to modify the rotational position of beam directorelements 420 and re-position the alignment beam within the sensor. Theposition of the alignment beam is then once again measured by opticalsensor 422, and the adjustment to the rotational positions of the beamdirecting elements is repeated if necessary. By properly positioning thealignment beam in this manner, the proper position of the communicationbeam is achieved without any interference with or measurement of thecommunication beam itself.

Example of Operation of the Invention

In operation, the preferred switch of the present invention transmits anoptical signal from an input fiber in bundle 4 to an output fiber inbundle 6. The operation of a preferred embodiment of the presentinvention is perhaps best understood with reference to FIGS. 1A and 1B.

Reconfiguration of the input-output mapping of fibers, the switchfabric, is accomplished as follows. Upon receipt of a reconfigurationcommand, the beam steering mirrors of the affected channels immediatelyperform an open loop step, moving from their current position to a newposition appropriate for completing the commanded reconfiguration.During the open loop step, control feedback is terminated on theaffected channels. When the beam steering elements are near their newpositions, the alignment beam falls on the portion of the sensorcorrespond to the new output fiber indicated by the configurationcommand. At this point, closed loop servo control is re-initiated andthe new connection is finalized. During the open loop step, thealignment beam for all the other repositioning channels may be switchedoff in order to eliminate any contamination of the servo feedback signalof non-switched channels by the guidance beams of the switchingchannels.

In a preferred embodiment, the servo loop may operate only on the mirrorelements in the second mirror array. In alternative embodiments, theservo loop may operate on the mirror elements in the first mirror array,the second mirror array, or both the first and second mirror arrays. Inone embodiment, the calibration of each of the mirror elements in thefirst array is sufficiently accurate that it is possible to positionthese elements with an open loop signal such that substantially all ofthe optical energy of the alignment and communications beamscorresponding to each element will fall on the intended target mirrorelement in the second beam director array. The open loop pointing of thebeam directing mirror elements is calibrated at manufacture, andperiodically throughout the lifetime of the device, insuring that theopen loop pointing accuracy is high. Also, the open loop pointingaccuracy of the mirrors in the first array needs to be no better than afew percent of the full stroke since small errors in position of thefirst elements are, in effect compensated by the closed loop servocontrol system operating on elements in the second mirror array. Thisinitial open loop pointing, in combination of the feedback control ofthe second beam directing elements accurately positions thecommunication beam onto the center of the output fiber.

Multiplexing and De-Multiplexing

An important application of the switch described above is as a part of afrequency multiplexing or de-multiplexing operations. As explained abovemultiplexing typically involves adding signals at specific frequenciesto a trunk line optical fiber carrying other frequencies andde-multiplexing is the opposite. In each case switches are needed todirect the resulting optical signals into the desired direction,typically separate optical fibers. Several multiplexing andde-multiplexing techniques are available as discussed in the backgroundsection including the use of thin film filters. However, Applicantspreferred multiplexing/de-multiplexing technique is one that they havedeveloped that provides substantial advantages over prior arttechniques. This technique utilizes porous silicon optical filters. Thistechnique produces results very similar to thin film filters, but theporous silicon filters can be produced much quicker and with much lessexpense. A short summary description of these porous silicon opticalfilters is provides below and pictured in FIGS. 12A and 12B.

Porous Silicon Optical Filters

FIG. 12A is a depiction of a portion of a silicon wafer with six layersof varying index of refraction etched in its surface with an electriccurrent supported acid etch porous silicon technology. Porous silicon(PSi) technology is an emerging technology that has many potentialapplications. A silicon wafer is submerged in hydrofluoric acid (HF) anda current is passed through it. The HF reacts with the silicon andetches nano-pores into the surface. The diameter of the pores isdetermined by 3 parameters: the current, the HF concentration, and thedopant level of the silicon. Preferred HF concentrations are in therange of about 25 percent to about 50 percent. Preferred silicon dopingis about 2.5×10¹⁶ ions/cm³ to about 2.5×10¹⁷ ions/cm³. The etchingalways occurs at the interface between the HF solution and the siliconsubstrate at the bottom of the pores. This makes it possible to etchdeep into the silicon and form a thick layer of PSi. The diameter of thepores can be changed during the etching process by varying the current.A larger current increases the diameter of the pores, and a smallercurrent decreases their diameter. In this manner the porosity of thesilicon can be varied as a function of depth. Larger porosity (largerdiameter pores) makes the silicon less dense which decreases the indexof refraction of the PSi layer. And smaller porosity increases theindex. Hence, the index of refraction of the PSi can be varied. Thisability to vary the index as a function of depth enables the formationof optical filters. FIG. 12B is a drawing showing the general shape ofthe pours (produced in a silicon substrate 48) greatly magnified in asurface simulating 12 layers. Silicon has an index of refraction ofabout 3.5 and air has an index of refraction of about 1.00. Since thelight we are concerned with has wavelengths much larger than the pores,the light responds to each simulated layer as if it had an index ofrefraction equal to the weighted average of the air and the siliconvolume making up each layer. For example, a low index of refraction isindicated at 51 and a high index of refraction is indicated at 53. FIG.12C shows a graph of current and time utilized to produce the patternshown in FIG. 12B and FIG. 12D shows the reflectance from the surface oflight at wavelengths of 820 nm to 850 nm. This filter was made with 24layers as indicated in FIG. 12C. The filter can be made narrower byadditional layers. FIG. 12E shows the results with 29 layers. FIG. 12Fis a reflection graph of a porous silicon designed for the wavelengthrange regularly used for fiber optic communication.

Rugate Porous Silicon Filters

The types of filter that can be formed in PSi is intriguing. Traditionalthin-film filters are made by alternating between thin (quarter-wavethick) layers of a high index material and a low index material. In PSithe index variation oscillates continuously between a high and a lowvalue. This type of filter is called a “Rugate filter”. Some interestingeffects can be achieved, such as eliminating unwanted side-lobes from anarrow band-pass filter. FIG. 12G shows porosity vs depth in the waferof a Rugate filter made by Applicants and FIG. 12H shows the resultingreflection profile as a function of wavelength. The graph shows threevery narrow transmission bands.

FIGS. 12I and 12J show how porous silicon filter unit can be arrangedfor multiplexing and de-multiplexing. FIG. 12I shows four fibers 54providing an incoming communication beam comprising many signals atwavelength bands λ₁, λ₂ . . . λ_(n). Porous silicon filters designed totransmit individual wavelength are shown at 56. For example, filter 56Atransmits wavelength range λ₁ and reflects all other wavelength bands.Filter 56B transmits another wavelength band and reflects all otherwavelength bands. The wavelength bands are focused into individualoptical fiber by lens arrays 58. This design as shown in FIGS. 12I and12J uses a series of very narrow-band filters to sequentially separateone wavelength channel at a time from the DWDM beam. At each filter theselected channel is transmitted and the remaining wavelengths arereflected. If visible light is used the silicon substrate may be thinnedor removed so that the transmitted light is not completely absorbed. Formost optical telecommunications applications silicon is basicallytransparent to the wavelengths used and the silicon substrate may remainif the doping concentration is not too high. This filtering technique isconceptually simple but may not be the best for DWDM systems with alarge number of wavelength channels since the final wavelength mustencounter N−1 (N is the total number of wavelength channels in the DWDMbeam) filters before it is separated from all other wavelengths. Morecomplicated designs can reduce the total number of filters that any onebeam must pass through by having the first several filters transmit morethan one wavelength channel. Narrowband filters may then be used toseparate the individual wavelength channels from the decimated beams.

Many different prior art Rugate filter designs developed for thin filmfilters can be used with the porous silicon technique to achieve anarrowband filter with the specifications required for DWDM use. Withthe porous silicon technique Applicants can simulate stacks of thin filmfilters by producing multiple series of varying index layers that varysinusoidally. This is equivalent to the fabrication of two or morerelatively broadband reflectors on top of each other. This configurationis the Rugate filter equivalent to the multi-cavity filters found incommercial, discrete, thin-film dielectric filters. This type filter canachieve extremely good wavelength resolution without prohibitive lengthdue to its emulation of Fabry-Perot etalon resonant cavities.

Stacking the filters on top of each other produces index of refractionprofile that is extremely high across the C band except for a few verynarrow wavelength regions that correspond to the resonant bands of thecombined filter structure. This is where the phase change ontransmission through the broadband filter matches the phase change onreflection from the second broadband filter. The exact wavelength andwidth of these transmission regions can be controlled, within a limitedrange by the design of the length and index profile of the broadbandreflective filters.

Detection of Secret Wavelength

The present invention can be easily adapted to detect the presence of atracker wavelength. These special tracker wavelengths can be added to acommunication beam in order to track the beam as it makes its waythrough a completed optical route. The present invention can easily beprogrammed to periodically extract beams in each fiber to direct it to atesting unit to test for the tracker wavelength.

Adjusting Beam Intensity

Another useful application of the present invention is that it can beeasily programmed to adjust the intensity of particular beams. It isimportant in communication systems that the intensity of various beamsin a system be relatively uniform in intensity, especially just prior toamplification. The present invention can easily reduce the intensity ofany beam passing through the switch by merely slightly misaligning thebeam using units 16 and 18 to provide just the desired amount ofmisalignment. The more the beam is misaligned the more the beam isattenuated because smaller portions of it are focused into the outputfiber.

Other Sizes

In the present embodiment, the configuration is an 8×16 array designedto be used to connect 8×16 fiber optic bundles. However, readers shouldappreciate that the present invention may be scaled to many other sizes,smaller or larger, without any significant increase in complexity of themanufacturing, alignment, or corresponding control system. Alsoadditional or fewer spare channels may be provided based on experience.

Other Variations

While there have been shown what are presently considered to bepreferred embodiments of the present invention, it will be apparent tothose skilled in the art that various changes and modifications can bemade herein without departing from the scope and spirit of theinvention. For example, the switch shown in FIG. 1A could be scaled upor down as desired. The field programmable gate arrays used to controlthe mirrors can be replaced with more economical integrated circuits.The MEMS mirrors may be controlled with other variable voltage sourcesand larger capacitors could be utilized. Many types of automaticcontrols can be incorporated into the switches or used to control theswitches. Filters other than porous silicon filters such as thin filmfilters could be used for multiplexing and de-multiplexing. Fewer ormore or zero spare channels could be provided. The source of thealignment beam may be a resonant cavity light emitting diode. In someembodiments alternate alignment techniques could be used. Many othertechniques are available for aligning an alignment beam with thecommunication beam in each fiber of the switch. There are many alternatemethods of arranging the incoming fibers in the input portion of theswitch. Small mirror arrays other than MEMS mirror arrays could besubstituted for the MEMS mirror arrays. One processor could be usedinstead of the two shown in FIGS. 1A and 1B. There are a large number ofapplications for the present invention other than the two important onesdiscussed in detail. For example, the switch could be used in localintra-office or intra-factory communication systems where very high datarate communication is important. Signal grooming features, gain controland amplifiers could be incorporated into the switch. ROADM units of thepresent invention can be used to support express local and regionalcommunication traffic. The switch of the present invention can beutilized in all of the system architectures including point-to-point,ring (hubbed and meshed). Therefore, the scope of the patent should bedetermined by the appended claims and their legal equivalence and not bythe examples that have been given.

1. A fiber-microlens positioning array comprising; A) a plurality ofoptical fibers at least partially contained in a smaller plurality offiber optic ribbons, B) a mounting plate adapted to permit the passagethrough the mounting plate of said optical fibers extending from saidfiber optic ribbons, C) a positioning plate comprised of a singlesilicon plate mounted on said mounting plate comprising a twodimensional array of lithographically-defined V-grooves for alignment ofsaid plurality of optical fibers extending from said fiber optic ribbonsto provide an array of optical fiber beam exit and/or entranceapertures, wherein each of said V-grooves are positioned in said singleplate both horizontally and vertically with sub-micron accuracy, andwherein said plurality of optical fibers extending from said pluralityof fiber optic ribbons are fixedly positioned in the V-grooves and D) amicrolens array comprised of a plurality of microlenses positioned toalign a microlens with each optical fiber beam exit and/or entranceaperture in said array of optical fiber beam exit and/or entranceapertures.
 2. A method for forming an array of optical fiberscomprising: A) providing a mounting plate adapted to permit the passagethrough the mounting plate of said optical fibers extending from fiberoptic ribbons, B) mounting on said mounting plate a positioning platecomprised of a single silicon plate comprising an array oflithographically-defined V-grooves positioned with sub-micron accuracy,C) inserting optical fibers extending from said fiber optic ribbonsthrough said mounting plate and into the V-grooves, D) fixing the fibersin the V-grooves, and E) positioning a microlens array comprised of aplurality of microlenses to align a microlens with each optical fiberbeam exit and/or entrance aperture in said array of optical fiber beamexit and/or entrance apertures to provide a fiber-micro lens positioningarray.
 3. The fiber-microlens positioning array as in claim 1 whereinsaid array of optical fiber beam exit and/or entrance apertures is anarray of optical fiber beam exit apertures.
 4. The fiber-microlenspositioning array as in claim 1 wherein said array of optical fiber beamexit and/or entrance apertures is an array of optical fiber beamentrance apertures.
 5. The fiber-microlens positioning array as in claim1 wherein said array of optical fiber beam exit and/or entranceapertures is an array of optical fiber beam exit and entrance apertures.6. The fiber-microlens positioning array as in claim 1 wherein saidfiber-microlens positioning array is adapted to produce an array ofparallel collimated light beams.
 7. The fiber-microlens positioningarray as in claim 1 wherein said array is adapted to produce an array ofparallel collimated cross-connect communication beam paths.
 8. Thefiber-microlens positioning array as in claim 7 wherein each of saidcommunication beam paths connects each of said exit and/or entranceaperture with a MEMS mirror.
 9. The fiber-microlens positioning array asin claim 1 wherein said plurality of optical fiber ribbons is aplurality of 8-fiber ribbons.
 10. The fiber-microlens positioning arrayas in claim 1 wherein said plurality of ribbons is 16 ribbons.
 11. Thefiber-microlens positioning array as in claim 7 wherein said microlensarray is a lithographically fabricated microlens array.
 12. Thefiber-microlens positioning array as in claim 7 wherein each of saidmicrolenses in the microlens array has a diameter of about 1.1millimeters and a focal length of about 3.7 millimeters.
 13. Thefiber-microlens positioning array as in claim 7 wherein said microlensarray is spaced away from said array of exit and/or entrance aperturesso as to create a beam waist approximately at a desired location foreach beam path.
 14. The fiber-microlens positioning array as in claim 7wherein said fiber-microlens positioning array and a similarfiber-microlens positioning array are components in an optical switchmodule for cross connecting optical fibers in a first set of opticalfibers to optical fibers in a second set of fibers, said optical switchmodule comprising: A) a first MEMS mirror array comprising an array ofMEMS mirrors arrayed in a first MEMS mirror pattern corresponding tosaid first fiber-microlens array pattern and positioned to reflectcommunication light beams to and/or from optical fibers arrayed in saidfirst fiber-microlens positioning array and a second MEMS mirror arraycomprising an array of MEMS mirrors arrayed in a second MEMS mirrorpattern corresponding to said second fiber-microlens array pattern andpositioned to reflect communication light beams to and/or from opticalfibers arrayed in said second fiber-microlens positioning array, B) afirst alignment beam unit for providing an alignment beam for eachcommunication beams between said first fiber-microlens array and saidfirst MEMS array and co-aligning said alignment beams with thecommunication light beams, defining a first set of alignment beams, anda second alignment beam unit for providing an alignment beam for eachcommunication beams between said second fiber-microlens array and saidsecond MEMS array and co-aligning said alignment beams with thecommunication light beams, defining a second set of alignment beams, C)a dichroic mirror positioned and adapted to reflect communication beamsfrom said first MEMS array to said second MEMS array and/or to reflectcommunication beams from said second MEMS array to said first MEMS arrayand to transmit said first and second set of alignment beams, D) a firstbeam direction sensor positioned and adapted to sense directions of eachalignment beam in said first set of alignment beams transmitted throughsaid dichroic mirror and a second beam direction sensor positioned andadapted to sense directions of each alignment beam in said second set ofalignment beams transmitted through said dichroic mirror, and E) a MEMScontrol system for controlling positions of each mirror in said firstand second MEMS mirror arrays in order to provide optical connectionsbetween each of the mirrors in said first set of optical fibers and anyfiber in said second set of optical fibers and/or to provide opticalconnections between each of the mirrors in said second set of opticalfibers and any fiber in said first set of optical fibers.